1. Field of the Invention
This invention relates to a semiconductor device having a semiconductor body, comprising a surface-adjoining region of the first conductivity type, a current conductor of which at least a part comprises a surface-adjoining strip-shaped semiconductor zone of the second conductivity type, and, on at least one side of the strip-shaped semiconductor zone, at least one surface-adjoining further zone of the second conductivity type which is separated from the strip-shaped semiconductor zone by a part of the region of the first conductivity type and which forms part of a semiconductor circuit element, in which, in order to reduce the voltage drop across the current conductor as much as possible, the strip-shaped semiconductor zone, in as far as it forms part of said part of the current conductor, is covered substantially throughout its surface by a metal layer and is contacted with said metal layer at least at the ends of the current conductor, in which at least one conductor track, crosses the said part of the current conductor and the said metal layer is interrupted at the area of the crossing, the resulting parts of the metal layer contacting the strip-shaped semiconductor zone at least at their ends. The invention also relates to a method of manufacturing such a semiconductor device.
"End" should not be understood to mean the strictly goemetric end of the current conductor or of parts of the metal layer, but regions of said semiconductor and metal layer, respectively, in the proximity of said goemetric end. It will also be obvious that the current conductor may form part of a larger assembly, for example a conductor track, in which the voltage drop in the regions outside the current conductor meant here is bound to less stringent requirements.
2. Description of the Prior Art
A semiconductor device as described above is known, for example, from U.S. Pat. Nos. 4,056,810 and U.S. Pat. No. 4,078,208, the contents of which should be deemed to be incorporated in the present application.
The said Patent describes a semiconductor device comprising a surface-adjoining region of the first conductivity type, a current conductor comprising a surface-adjoining strip-shaped semiconductor zone of the second conductivity type and several surface-adjoining further zones of the second conductivity type which are separated from the strip-shaped semiconductor zone by a part of the region of the first conductivity type. The strip-shaped semiconductor zone, the intermediate region and the further zones serve in the said patent as an emitter, base and collector of a lateral transistor. Said transistor (injector) ensures the current supply for a number of vertical transistors the bases of which constitute the collectors of the injector. Moreover, each of the vertical transistors can comprise several collectors; herewith circuits of the so-called integrated injection logic type are realized.
For the sake of a uniform current supply of the said vertical transistors throughout the length of the strip-shaped semiconductor zone, it is therefore desired that said strip-shaped semiconductor zone should have a constant potential within very narrow tolerances. However, said semiconductor zone has a certain resistance; the sheet resistance of such a semiconductor zone may be, for example, 200 ohms per square. Since said strip-shaped semiconductor zone may be very long and should be capable of supplying current to many of the above vertical transistors, an undesired potential drop can easily occur in said strip-shaped zone. As a result of this, the voltage between the strip-shaped semiconductor zone and the region of the first conductivity type is no longer constant and irregular current supply to the vertical transistors may occur so that the switching behaviour of the said transistors is adversely influenced.
This drawback has been partly mitigated in the above-mentioned patents by covering the strip-shaped semiconductor zone with a metal layer which contacts said strip-shaped semiconductor zone over substantially the whole length of the semiconductor zone. The current conductor formed in this manner has a resistance which is considerably lower than that of the strip-shaped semiconductor zone alone. As a result of this, the voltage drop in the case of current supply is considerably reduced.
Although this measure is already an important improvement, not all the drawbacks have been removed herewith.
In the case of large numbers of circuit elements within one semiconductor device it is actually often necessary to provide conductive connections which cross a current conductor as mentioned above. For this purpose it is necessary to interrupt the metal layer above the strip-shaped semiconductor zone at the area of the crossing so that the current conductor at the area of the crossing consists exclusively of the strip-shaped semiconductor zone.
Although this is the case only over a short distance, the resulting higher resistance at the crossing nevertheless gives rise in many cases to an unacceptably large voltage drop along the strip-shaped semiconductor zone.
Of course, the said problems may present themselves also in other types of circuits, in which current conductors are used which comprise semiconductor zones coated with a metal layer and which are crossed by other conductor tracks described, for example, in U.S. Pat. No. 3,525,020, and in general in all cases in which the voltage drop along similar current conductors should be extremely small.
One of the objects of the invention is to avoid the above-mentioned drawbacks entirely or at least as much as possible.